Implemented custom Error and Result types to be returned

Like a good library ought to be, Pumpkin now returns actual Errors, rather
than panicking.

src/common.rs

@@ -1,6 +1,8 @@
 use ramp::{Int, RandomInt};
 use rand::{OsRng, thread_rng};
 
+use error::{Error, Result};
+
 static SMALL_PRIMES: [u32; 999] = [3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59,
                                    61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127,
                                    131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191,
@@ -101,45 +103,46 @@ static SMALL_PRIMES: [u32; 999] = [3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41,
 
 /// Constructs a new prime number with the size of `bit_length` bits, sourced
 /// from an already-initialized `OsRng`.
-pub fn gen_prime(bit_length: usize, rngesus: &mut OsRng) -> Int {
-    debug_assert!(bit_length >= 512);
-    let mut candidate: Int;
+pub fn gen_prime(bit_length: usize, rngesus: &mut OsRng) -> Result {
+    if bit_length < 512 {
+        Err(Error::BitLength(bit_length))
+    } else {
+        let mut candidate: Int;
 
-    // In order to remove as much bias from the system as possible, test
-    // 500 potential candidates at a time before re-seeding the candidate
-    // with a new random number.
-    loop {
-        let mut counter = 0;
-        let mut found_prime = true;
-        candidate = rngesus.gen_uint(bit_length);
+        // In order to remove as much bias from the system as possible, test
+        // 500 potential candidates at a time before re-seeding the candidate
+        // with a new random number.
+        loop {
+            let mut counter = 0;
+            let mut found_prime = true;
+            candidate = rngesus.gen_uint(bit_length);
 
-        // We first want to make sure that the candidate is in the appropriate
-        // size range before continuing. This can easily be done by setting the
-        // two most significant bits of the candidate number to 1.
-        candidate.set_bit(bit_length as u32, true);
-        candidate.set_bit((bit_length-1) as u32, true);
+            // We first want to make sure that the candidate is in the appropriate
+            // size range before continuing. This can easily be done by setting the
+            // two most significant bits of the candidate number to 1.
+            candidate.set_bit(bit_length as u32, true);
+            candidate.set_bit((bit_length-1) as u32, true);
 
-        // Next, flip the least significant bit to 1, to make sure the candidate
-        // is odd (no sense in testing primality on an even number, after all).
-        candidate.set_bit(1, true);
+            // Next, flip the least significant bit to 1, to make sure the candidate
+            // is odd (no sense in testing primality on an even number, after all).
+            candidate.set_bit(1, true);
 
-        // Now run through the actual primality check!
-        while !is_prime(&candidate) {
-            candidate += 2_usize;
-            counter += 1;
+            // Now run through the actual primality check!
+            while !is_prime(&candidate) {
+                candidate += 2_usize;
+                counter += 1;
 
-            if counter > 499 {
-                found_prime = false;
-                break;
+                if counter > 499 {
+                    found_prime = false;
+                    break;
+                }
+            }
+
+            if found_prime {
+                return Ok(candidate);
             }
         }
-
-        if found_prime {
-            break;
-        }
     }
-
-    candidate
 }
 
 /// Runs the following three tests on a given `candidate` to determine

src/error.rs

@@ -0,0 +1,46 @@
+use ramp::Int;
+use std::{error, fmt, io, result};
+
+pub type Result = result::Result<Int, Error>;
+
+#[derive(Debug)]
+pub enum Error {
+    OsRngInitialization(io::Error),
+    BitLength(usize)
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Error::OsRngInitialization(ref err) => {
+                write!(f,
+                    "Error initializing the random number generator: {}",
+                    err
+                )
+            },
+            Error::BitLength(length) => {
+                write!(f,
+                    "The given bit length is too small; must be at least 512: {}",
+                    length
+                )
+            }
+        }
+    }
+}
+
+impl error::Error for Error {
+    fn description(&self) ->  &str {
+        match *self {
+            Error::OsRngInitialization(ref err) => err.description(),
+            Error::BitLength(_) => {
+                "The given bit length was less than 512"
+            }
+        }
+    }
+}
+
+impl From<io::Error> for Error {
+    fn from(err: io::Error) -> Error {
+        Error::OsRngInitialization(err)
+    }
+}

src/lib.rs

@@ -54,6 +54,7 @@ extern crate rand;
 extern crate test;
 
 mod common;
+mod error;
 pub mod prime;
 pub mod safe_prime;
 

src/prime.rs

@@ -1,9 +1,9 @@
 //! Generates cryptographically secure prime numbers.
 
-use ramp::Int;
 use rand::OsRng;
 
 pub use common::gen_prime as from_rng;
+use error::{Error, Result};
 
 /// Constructs a new prime number with a size of `bit_length` bits.
 ///
@@ -11,40 +11,22 @@ pub use common::gen_prime as from_rng;
 /// `from_rng()` function.
 ///
 /// Note: the `bit_length` MUST be at least 512-bits.
-pub fn new(bit_length: usize) -> Int {
-    assert!(bit_length >= 512);
-    let mut rngesus = match OsRng::new() {
-        Ok(rng) => rng,
-        Err(reason) => panic!("Error initializing RNG: {}", reason),
-    };
-
-    from_rng(bit_length, &mut rngesus)
+pub fn new(bit_length: usize) -> Result {
+    if bit_length < 512 {
+        Err(Error::BitLength(bit_length))
+    } else {
+        let mut rngesus = try!(OsRng::new());
+        Ok(try!(from_rng(bit_length, &mut rngesus)))
+    }
 }
 
 #[cfg(test)]
 mod tests {
-    use ramp::Int;
-    use super::{fermat, miller_rabin};
-
-    #[test]
-    fn test_fermat_pass() {
-        assert!(fermat(&Int::from(7919)));
-    }
+    use super::{new, from_rng};
 
     #[test]
     #[should_panic]
-    fn test_fermat_fail() {
-        assert!(fermat(&Int::from(7920)));
-    }
-
-    #[test]
-    fn test_miller_rabin_pass() {
-        assert!(miller_rabin(&Int::from(7919), 5));
-    }
-
-    #[test]
-    #[should_panic]
-    fn test_miller_rabin_fail() {
-        assert!(miller_rabin(&Int::from(7920), 5));
+    fn test_prime_bad_bit_length() {
+        new(511);
     }
 }

src/safe_prime.rs

@@ -4,6 +4,7 @@ use ramp::Int;
 use rand::OsRng;
 
 pub use common::{gen_prime, is_prime};
+use error::{Error, Result};
 
 /// Constructs a new `SafePrime` with a size of `bit_length` bits.
 ///
@@ -11,37 +12,35 @@ pub use common::{gen_prime, is_prime};
 /// `SafePrime::from_rng()` method.
 ///
 /// Note: the `bit_length` MUST be at least 512-bits.
-pub fn new(bit_length: usize) -> Int {
-    debug_assert!(bit_length >= 512);
-    let mut rngesus = match OsRng::new() {
-        Ok(rng) => rng,
-        Err(reason) => panic!("Error initializing RNG: {}", reason),
-    };
-
-    from_rng(bit_length, &mut rngesus)
+pub fn new(bit_length: usize) -> Result {
+    if bit_length < 512 {
+        Err(Error::BitLength(bit_length))
+    } else {
+        let mut rngesus = try!(OsRng::new());
+        Ok(try!(from_rng(bit_length, &mut rngesus)))
+    }
 }
 
 /// Constructs a new `SafePrime` with the size of `bit_length` bits, sourced
 /// from an already-initialized `OsRng`.
-pub fn from_rng(bit_length: usize, mut rngesus: &mut OsRng) -> Int {
-    debug_assert!(bit_length >= 512);
-    let mut candidate: Int;
+pub fn from_rng(bit_length: usize, mut rngesus: &mut OsRng) -> Result {
+    if bit_length < 512 {
+        Err(Error::BitLength(bit_length))
+    } else {
+        let mut candidate: Int;
 
-    // Circumvent uninitialized warning (technically valid but compiler
-    // cannot determine that `clone_from` will fill the value.
-    let mut candidate_p: Int = Int::zero();
+        loop {
+            candidate = try!(gen_prime(bit_length, &mut rngesus));
 
-    loop {
-        candidate = gen_prime(bit_length, &mut rngesus);
+            let mut candidate_p = (&candidate).clone();
+            candidate_p -= 1_usize;
+            candidate_p /= 2_usize;
 
-        candidate_p.clone_from(&candidate);
-        candidate_p -= 1_usize;
-        candidate_p /= 2_usize;
-
-        if is_prime(&candidate_p) {
-            break;
+            if is_prime(&candidate_p) {
+                break;
+            }
         }
-    }
 
-    candidate
+        Ok(candidate)
+    }
 }